The working hypothesis that butyrylcholinesterase (BuChE) functions as a precursor and regulator of the rate of synthesis of acetylcholinesterase (AChE) will be tested by electron and light microscopic (EM and LM) histochemical, biochemical, and pharmacological investigation. The identity of the neurotrophic factor(s) responsible for the maintenance of ganglionic AChE and BuChE will be sought. EM studies of this distribution of AChE and BuChE at various sites will be continued. BIBLIOGRAPHIC REFERENCES: Ruch, G.A., Davis, R., and Koelle, G.B.: The Acetylcholinesterase and Pseudocholinesterase Contents of Human Placenta at Term. Journal of Neurochemistry, 26: 1189-1192, 1976. Koelle, G.B.: The Neuropharmacologist's Dilemma. Perspectives in Biology and Medicine, 19: 402-403, 1976.